Genotype diversity and antibiotic resistance risk in Aeromonas hydrophila in Sichuan, China

Abstract

Sichuan is a significant aquaculture province in China, with a total aquaculture output of 1.72 × 10⁶ tons in 2022. One of the most significant microorganisms hurting the Sichuan aquaculture is Aeromonas hydrophila, whose genotype and antibiotic resistance are yet unknown. This study isolated a total of 64 strains of A. hydrophila from various regions during September 2019 to June 2021 within Sichuan province, China. The technique of Multi-Locus Sequence Typing (MLST) was used for the purpose of molecular typing. Meanwhile, identification of antibiotic resistance phenotype and antibiotic resistance gene was performed. The findings of the study revealed that 64 isolates exhibited 29 sequence types (ST) throughout different regions in Sichuan, with 25 of these ST types being newly identified. Notably, the ST251 emerged as the predominant sequence type responsible for the pandemic. The resistance rate of isolated strains to roxithromycin was as high as 98.3%, followed by co-trimoxazole (87.5%), sulfafurazole (87.5%), imipenem (80%), amoxicillin (60%), and clindamycin (57.8%). Fifteen strains of A. hydrophila exhibited resistance to medicines across a minimum of three categories, suggesting the development of multidrug resistance in these isolates. A total of 63 ARGs were detected from the isolates, which mediated a range of antibiotic resistance mechanisms, with deactivation and efflux potentially serving as the primary mechanisms of antibiotic resistance. This study revealed the diversity of A. hydrophila genotypes and the risk of antibiotic resistance in Sichuan, providing reference for scientific and effective control of A. hydrophila infection.

Keywords: Aeromonas hydrophila; Antibiotic resistance gene; Antibiotic resistance phenotype; Aquatic animal; MLST.

Fig. 1

Pathological changes and identification of A. hydrophila. A Carassius auratus (top picture) has bleeding on its body, whereas Ictalurus punctatus (bottom image) has congestion, enteritis, and ascites. B The pink and short rod-shaped A. hydrophila can be seen under a microscope. C Results of a dual PCR on the 16S rRNA gene and the gyrB gene in A. hydrophila

Fig. 2

Source statistics of 64 isolated A. hydrophila. A Period statistics of isolated strains. The rate of isolation throughout spring and summer was 32.81%, followed by autumn (31.24%), and winter (3.13%). B Host statistics of isolated strains. The isolation rate of A. hydrophila in Ictalurus punctatus was 23.44%, followed by Acipenser sinensis (21.88%), and Pelteobagrus fulvidraco (18.75%). C Geographic distribution of isolated strains. The locations of all isolates over the three years are shown on the map. D Location statistics of isolated strains. Chengdu, Leshan, and Meishan have high isolation rates, while the remaining areas have low isolation rates

Fig. 3

Phylogenetic tree based on 29 ST types of isolated strains (https://www.chiplot.online/tvbot.html). There were a total of 29 ST types, out of which only four ST types were known. These ST types were further categorized into four distinct clusters, namely A, B, C, and D. The graphic also depicted the distribution of each ST type in each location

Fig. 4

The antibiotic resistance profiles of 64 isolated A. hydrophila. A Distribution of resistance in all A. hydrophila. The graphic presented the resistance of all isolates to each medication. B Statistics of the classification of 20 antibiotics. C Multidrug resistance of isolated strains. There were 7 strains with resistance to 3 drug categories, 7 strains with resistance to 4 drug categories, and 1 strain with resistance to 5 drug categories

Fig. 5

Circle diagram of resistance gene categories and strains. The resistance gene categories seen in this study, including beta-lactams, aminoglycosides, multiple medicines, tetracyclines, mobile genetic elements (MGEs), and resistance to Pb and Cu, among others. Beta-lactam antibiotics, aminoglycosides, a combination of medicines, and tetracyclines were administered in a greater percentage